The stresses both active and passive in cardiac ventricles are distributed by collagen, if the heart is analagous to skeletal muscle. The collagen matrix of skeletal muscle is a stress resistant structure with visco-elastic properties. Again, if the collagen matrix of the heart is analagous to skeletal muscle, alteration of the matrix will affect myocardial function. Recently we have observed that in the region of ischemia following coronary artery ligation there is near complete loss of the collagen matrix in the heart within three hours. By examining selected areas of the ischemic region using laser digital imaging to determine the strain rate, we demonstrated a very early (15 min.) increase in strain rate coincident with the loss of contraction. The strain rate remained at a plateau until 2 hrs after occlusion at which time it rose to 2.5 times control value. This rise is coincident with the loss of the collagen matrix. The goals of this proposal are to determine the material properties of the ventricle by laser digital imaging following coronary artery ligation until reasonable recovery occurs at two months. The digital image data will be correlated with histologic evaluation, both light microscopic and scanning electron microscopic, to determine the alterations in tissue constituents that contribute to abnormal material properties. This information will be compared with comparable information derived from animals with reflow after 3 hours of occlusion and reflow with streptokinase. This information may assist in understanding the mechanisms by which reflow of occluded coronary arteries on occassion is a deleterious procedure. The long term goals are to improve methods for obtaining information concerning material properties of the heart and use these in a variety of diseases associated with altered ventricular compliance to explain this phenomenon.